Minimum Changes for Palindromic Length-k Substrings

Given a password string s of length n and an integer k, one operation replaces any character with any lowercase English letter. Find the minimum number of replacements needed so that every contiguous substring of length exactly k is a palindrome. This formulation interprets “every k characters” as every sliding contiguous substring of length k. A version that partitions the string into disjoint blocks of size k is a different problem. Input Format n k s 1 <= n <= 2 * 10^5 1 <= k <= n s contains lowercase English letters only. Output Format Print the minimum number of replacements. Example Input: 7 3 abacaba Output: 1 Example Input 7 3 abacaba Output 1